Final answer:
Huck knows when his father is back in town by observing fresh footprints in the snow.
Step-by-step explanation:
Huck knows when his father is back in town because of the footprints left in the snow. In Chapter 6 of The Adventures of Huckleberry Finn, Huck notices fresh footprints in the snow leading to his father's cabin.
The text states, 'I see a light and footprints; and there in the snow was his old size thirteen tracks...' This evidence shows that Huck is able to recognize his father's presence through the physical sign of footprints in the snow.